1. Field of Invention
The present invention relates to a printing device that performs the function of adjusting for deviation between the landing positions of ink droplets that are deposited on the outbound and return passes of the recording head during bidirectional printing in which the recording head discharges ink droplets of a plurality of different sizes to print an image on the print medium on both the outbound and return passes of the recording head. The invention also relates to a method of controlling the printing device, to a program, and to a recording medium.
2. Description of Related Art
FIG. 8 schematically describes a printing process executed by a printer with a bidirectional printing function according to the related art. This printer has a recording head 3 that is capable of discharging ink droplets of a plurality of sizes mounted on a carriage not shown, and prints images on a print medium (such as paper) 5 during both the outbound pass (also referred to as the “first pass”) and the return pass of the recording head 3.
Referring to FIG. 8, the print medium 5 is conveyed in the paper feed direction indicated by arrow A in the figure by means of a transportation mechanism disposed inside the printer. A carriage not shown on which the recording head 3 is mounted is disposed to move bidirectionally in the direction perpendicular to the paper feed direction of the paper 5 by means of a guide mechanism 7 that extends perpendicularly to the paper feed direction of the paper 5.
The left end of the range in which the recording head 3 can be moved bidirectionally by the guide mechanism 7 is referred to as the column 0 side, and the right end of this range is the column 80 side. The printing process in which the recording head 3 is driven to print while traveling in the direction from column 0 to column 80 as indicated by arrow P1 in the figure is referred to as “outbound printing” or printing on the outbound or first pass, and the printing process in which the recording head 3 is driven to print while traveling in the direction from column 80 to column 0 as indicated by arrow P2 in the figure is referred to as “return printing” or printing on the return pass. Printing results from the recording head 3 operating in both the outbound printing mode and the return printing mode, that is, in both directions.
FIG. 9 shows the image G1 printed on the print medium 5 on the outbound pass, and the image G2 printed on the return pass. The nozzles of the recording head 3 for discharging ink droplets are arranged in a row and column pattern, and dot lines are printed on a plurality of rows (7 rows in this example) in a single pass in both outbound and return directions.
Bidirectional printing on both outbound and return passes of the recording head 3 requires bidirectional adjustment (also called gap adjustment) to correct for deviation in the landing positions of the ink droplets discharged on the outbound and return passes. This deviation in the ink droplet landing positions on the outbound and return passes differs according to the dot size of the discharged ink droplets.
Japanese Unexamined Patent Appl. Pub. JP-A-2003-266700 teaches a printing control method that efficiently applies this bidirectional adjustment by selecting a dot of an intermediate size as the reference dot during both outbound and return passes, or selecting the reference dot for outbound and return passes based on the printing mode (such as a photographic print mode and a text print mode) selected for the print job, and applies the bidirectional adjustment to eliminate deviation in the land positions of the selected reference dot.
When printing images as shown in FIG. 10, however, there may be plural images of different basic types on a single page S, including illustrations Q1, a barcode Q2, text Q3, or a photograph Q4. When printing a photograph Q4, for example, ink droplets forming small and medium size dots are normally discharged to enable printing high resolution pictures with rich gray scale variation. When printing a barcode Q2, however, ink droplets forming large dots are typically discharged to enable printing sharp barcodes that are easy to read. The dot size yielding the best print result thus varies according to the characteristics of the image Q1 to Q4 being printed.
This means that if bidirectional adjustment is applied using a uniform medium size dot as the reference dot, or bidirectional adjustment is applied using a reference dot selected according to the print mode, the ink droplet landing position can be sufficiently corrected for some types of images but not for other types of images, and image degradation may result in parts.
For example, because the print mode is generally selected once for an entire file or for individual pages of the image data file to be printed, the print mode will be selected referenced to one of the images Q1 to Q4 when printing the image file shown in FIG. 10. However, if the print mode is set to the photographic mode based on the photographic image, the photograph Q4 can be printed with high resolution and no deviation in the ink droplet landing positions, but resolution will drop in the barcode Q2 and text Q3 images because of the deviation in the ink droplet landing positions.